Clarify a role of Shadow DOM related functions

third_party/WebKit/Source/core/html/HTMLContentElement.cpp

 /*
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Neither the name of Google Inc. nor the names of its
@@ skipping 58 matching lines @@
     m_shouldParseSelect = false;
     m_isValidSelector = validateSelect();
     if (!m_isValidSelector)
         m_selectorList = CSSSelectorList();
 }
 
 void HTMLContentElement::parseAttribute(const QualifiedName& name, const AtomicString& oldValue, const AtomicString& value)
 {
     if (name == selectAttr) {
         if (ShadowRoot* root = containingShadowRoot()) {
-            if (root->owner())
+            if (!root->isV1() && root->owner())

[kochi, 2016/09/09 06:51:06]

If <content> is in V1 shadow, we don't have to parser select= attribute at all?

i.e.

ShadowRoot* root = containingShadowRoot();

if (!root || root->isV1 || name != selectAttr) {
    InsertionPoint::parseAttribute(...);
    return;
}

// do the rest

[hayato, 2016/09/09 07:03:29]

Yeah, I am aware there are still a lot of TODO things.
I'll address them in bunch of follow-up CLs.

[kochi, 2016/09/09 07:06:58]

Sounds good.

                 root->owner()->willAffectSelector();
         }
         m_shouldParseSelect = true;
         m_select = value;
     } else {
         InsertionPoint::parseAttribute(name, oldValue, value);
     }
 }
 
 static inline bool includesDisallowedPseudoClass(const CSSSelector& selector)
@@ skipping 37 matching lines @@
     SelectorChecker::SelectorCheckingContext context(&element, SelectorChecker::VisitedMatchDisabled);
     for (const CSSSelector* selector = selectorList().first(); selector; selector = CSSSelectorList::next(*selector)) {
         context.selector = selector;
         if (checker.match(context))
             return true;
     }
     return false;
 }
 
 } // namespace blink